The present invention relates to a liquid crystal display device and a repair process for the same, more specifically to a liquid crystal display device disconnection of the bus lines of which can be repaired and a repair process for the same.
Recently, active matrix-type liquid crystal display devices are widely used in OA machines and tools, typically personal computers, and are larger-sized and more fined for the purpose of their application to EWS (Engineering WorkStations), etc.
However, there is a tendency that the bus lines for driving the TFTs (Thin-Film Transistors) of the picture elements are made longer for larger sizes of the liquid crystal display devices, and for further fineness of the liquid crystal display devices the bus lines are made thinner. Accordingly, the bus lines have higher possibility of being disconnected in the process of fabricating the bus lines.
A conventional liquid crystal display device, and a conventional repair process for repairing disconnected bus lines of the liquid crystal device will be explained with reference to FIG. 27. FIG. 27 is a plan view of the conventional liquid crystal display device.
As shown in FIG. 27, gate bus lines 112 are formed on a glass substrate 110, extended horizontally as viewed in the drawing, and data bus lines 120 are formed, crossing the gate bus lines 112.
A plurality of TABs (Tape Automated Bondings) 116a, 116b are adhered to the left margin of the glass substrate 110 as viewed in the drawing. Gate drivers 114a, 114b are formed respectively on the gate TABs 116a, 116b. The respective gate lines 112 are connected to the outputs of the gate drivers 114a, 114b. The gate TABs 116a, 116b are adhered to a print substrate 118.
On the other hand, a plurality of data TABs 124a to 124c are adhered to the lower margin of the glass substrate 110 as viewed in the drawing. Respective data drivers 122a to 122c are formed in the data TABs 124a to 124c. The respective data bus lines 120 are connected to the outputs of the data drivers 122a to 122c. The data TABs 124a to 124c are adhered to the print substrate 126.
Repair lines 134a to 134c are formed, crossing the data bus lines 120 below a display region 130 of the liquid crystal display device. The repair lines 134a to 134c are associated respectively with the data TABs 124a to 124c and are connected to lines (not shown) of the print substrate 126 via the data TABs 124a to 124c. 
On the other hand, repair lines 132a to 132c are formed, crossing the data bus lines 120 upper of the display region 130 of the liquid crystal display device. The repair lines 132a to 132c are extended to the right as viewed in the drawing corresponding respectively to the repair lines 134a to 134c. The repair lines 132a to 132c are connected to lines (not shown) of a print substrate 118 via the gate TAB 116a. 
The repair line 132a is connected to the repair line 134a via the print substrate 118, the connection cable 128 and the print substrate 126. Similarly therewith, the repair line 132b is connected to the repair line 134b, and the repair line 132c is connected to the repair line 134c. 
In the liquid crystal display device having such structure, when the data bus line 120 is disconnected at a line disconnected part 121, for example, the line disconnection has been repaired by the following process.
First, a laser beam is applied to a region where the data bus line 120a, which is upper of the line disconnected part 121 as viewed in the drawing, crosses the repair line 132c from the side of the glass substrate 110 to electrically connect the data bus line 120a to the repair line 132c. Thus, the data bus line 120a and the repair line 132c are connected to each other in a connection region 133a. 
Similarly therewith, the data bus line 120b, which is below the line disconnected part 121 as viewed in the drawing, and the repair line 134c are connected to each other, and the data bus line 120b and the repair line 134c are connected to each other in a connection region 133b. 
The data bus line 120a, which is upper of the line disconnected part 121 as viewed in the drawing, is brought into connection with the output of the data driver 122c because the repair line 132c and the repair line 134c are connected to each other in advance by the print substrate 118, the connection cable 128 and the print substrate 126, etc.
However, the above-described line disconnection repair is only for disconnection of the data bus lines 120 and cannot repair disconnection of the gate bus lines 112.
That is, in the normal gate bus line 112 without disconnection a gate signal has a time constant which increases away from the output of the gate drivers 114 as shown in FIG. 28A, and has waveforms of blunter rises and falls.
In contrast to this, in the above-described case that the disconnection of the gate bus line 112 is repaired, the gate bus line 112a and the gate driver 114 are connected to each other by the repair line 135 in a remotest region from the gate driver 114 without the intermediary of capacitance components, etc. in the display region 130. Accordingly, a signal waveform of the gate bus line 112a is adversely substantially the same as that of an output waveform of the gate driver 114.
Furthermore, as a gate signal comes nearer the disconnected line part 113 from the remotest region from the gate driver 114, the gate signal has a time constant increased and has waveforms of blunt rises and falls.
As a result, a signal waveform of the gate bus line 112a (see FIG. 28B) and a signal waveform (see FIG. 28A) of the normal gate bus line 112 adjacent to the gate bus line 112a are shifted with respect to each other. The shift between the signal waveforms of the gate bus line 112 and that of the gate bus line 112a causes the following potential shift between picture element electrodes. A mechanism for causing the potential shift between picture element electrodes adjacent to each other will be explained with reference to FIG. 29A and 29B.
As shown in FIG. 29B, when a gate signal Vg falls, a potential Vp of a picture element electrode 136 lowers by a potential difference xcex94Vs than a potential Vd of the data bus line 144.
A potential difference AVs is expressed by
xcex94Vs=Cgs/(Cgs+Cs+C1c)xc3x97(Vgonxe2x88x92Vgoff)
when a potential Vgon of the gate bus line 112 at the time that a gate signal is ON; a potential Vgoff of the gate bus line 112 at the time that a gate signal is OFF; a capacitance Cgs between the gate bus line 112 and the picture element electrode 136; a capacitance between the picture element electrode 136 and a Cs bus line 115 is Cs; and a capacitance between the picture element electrode 136 and an opposed electrode 117 is C1c.
Accordingly, when a potential Vg changes as indicated by the dot line in the gate bus line 112a having the disconnection repaired, and a potential Vg changes as indicated by the solid line in the normal gate bus line 112 adjacent to the gate bus line 112a, an effective value of Vgonxe2x88x92Vgoff differs between the gate bus line 112a having the disconnection repaired and the normal gate bus line 112 adjacent thereto. When an effective value of Vgonxe2x88x92Vgoff thus differs, a potential difference Vs differs, whereby the picture element electrode 136 connected to the gate bus line 112a having the disconnection repaired and the normal gate bus line 112 adjacent thereto have different potential Vp from each other. A potential Vp of the picture element electrode 136 influences luminance of display of the liquid crystal display device, with a result that a line defect is caused in display on the gate bus line 112a having the line disconnection repaired.
When a data bus line 120 has a line disconnection repaired, a waveform displacement takes place between the repaired bus line 120 and its adjacent normal data bus line 120. However, this causes no problem because a data signal Vd and a gate signal Vg are so timed that, as shown in FIG. 29B, the gate signal Vg falls after the data signal Vd has become constant, and a potential of a picture element electrode 136 is set.
The above-described conventional repair process for a liquid crystal display device requires the repair lines 132a to 132c, 134a to 134c be formed outside the display region 130, which requires a region for the repair lines 132a to 132c, 134a to 134c formed in. To this end a large space must be secured outside the display region 130, which has been a barrier to small-sizing the liquid crystal display device.
It often happens that insulation destruction of the insulation film due to static electricity between the repair lines 132a-132c and 134a-134c, and the data bus lines 120 crossing the repair lines, which is a factor for reducing fabrication yields of the liquid crystal display device.
It is necessary to form on the print substrates 118, 126, etc. lines for respectively interconnecting the repair lines 132a, 132b, 132c and the repair lines 134a, 134b, 134c, which is a factor for making the design complicated and resultantly a barrier to cost reduction of the liquid crystal display device.
In a case that because of the repair lines 132a-132c, 134a-134c, etc. a total line length is long, it is necessary to insert operational amplifiers, etc. in the lines.
An object of the present invention is to provide a liquid crystal display device a disconnection of a bus line of which can be repaired without degrading display characteristics, and a repair process therefor.
The above-described objects can be achieved by a repair process for a liquid crystal display device comprising a gate bus line, a data bus line crossing the gate bus line, a picture element electrode, and a transistor including a first electrode connected to the data bus line and a second electrode connected to the picture element electrode, the first electrode being extended along the gate bus line, in a case that the gate bus line has a line disconnection, that of the gate bus line on one side of the line disconnected part and the first electrode being connected, and that of the gate bus line on the other side of the line disconnected part being connected to the first electrode, whereby the line disconnected part of the gate bus line is repaired by the first electrode, and the first electrode being disconnected from the data bus line.
In the above-described repair process for a liquid crystal display device it is preferable that the first electrode is connected to the data bus line through a connection with a notch formed in, and the connection is disconnected at a region where the data bus line is thinned by the notch when the first electrode is disconnected from the data bus line. The notch partially thins the connection, whereby the connection can be disconnected for a short period of time. The notch apparently indicates a region to be disconnected, which improves efficiency of processing for disconnecting the connection.